This invention relates to a method for simultaneously tightening threaded fasteners to yield point, or to a point wherein predeterminded deformation of each fastener assembly occurs. Torque load is maintained until all fasteners are stressed to a predetermined point, at which time the power to all fastener setting tools is terminated.
While many different methods have been proposed and utilized for attainment of desired final torquing in fastener run-up and setting operations, the method of the present invention employs comparative change in areas under a curve developed by torque and angular rotation parameters. In such manner, errors associated with instantaneous reading, or arithmetical averages, of a torque angular rotation curve, are minimized. Consequently, final fastener yield point sensing is more accurately realized; power shut-off is initiated only after predetermined tension values are realized. In addition to tension control regulation, the invention incorporates certain "fail safe" features which guard against, (1) cross threaded fasteners, (2) galled fasteners, (3) broken fasteners, (4) no fasteners, and (5) low, or unacceptable, strength of an assembly.